The present invention relates to a fill limit vapor valve assembly for a vehicle fuel tank and, more particularly, to a fill limit vapor valve assembly that includes a bypass valve that varies the size of an opening in a housing skirt to control the flow rate of fuel vapor from the fuel tank as required to achieve the following: 1)minimize vapor flow from the tank during refueling xe2x80x9ctrickle-fillxe2x80x9d operations to prevent overfilling the fuel tank, and 2)maximize vapor flow from the tank after multiple xe2x80x9ctrickle-fillxe2x80x9d nozzle shutoffs (NSO""S) to minimize tank pressures after refueling operations.
The fill limit vapor valve (FLVV) assembly provided on current automotive fuel tanks typically has an internal fixed fuel vapor vent orifice to provide a flow passage from the fuel tank vapor space or dome to an emission apparatus, such as a charcoal canister, located external of the fuel tank. FLVV assemblies typically are designed with a mechanism to close the fixed fuel vapor vent orifice in the presence of liquid fuel, such as may occur at high static fuel levels in the fuel tank and from sloshing fuel in the fuel tank during vehicle movement. Closure of the fuel vapor vent orifice typically in the presence of liquid fuel at the valve assembly has been effected by a float biased with a spring load as required to achieve a buoyant force responsive to both static and dynamic fuel level changes. For instance, the float can have its upper region configured to include a nipple that when seated against the vent orifice will provide a liquid/vapor tight closure of the fuel vapor flow passage leading from the fuel vapor vent orifice to the charcoal canister.
The FLVV assembly (also commonly known as an ORVR valve assembly) includes a housing skirt configured with one or more upper flow windows located above the tank fuel level that is associated with 100% rated tank capacity. The size of the upper flow windows is used to control fuel level height at nozzle shutoff (NSO) during refueling operations and provide a flow passage through the housing skirt for fuel vapors when the bottom of the housing skirt is submerged in fuel.
Relatively large upper flow windows in the housing skirt are commonly used to minimize the difference in fuel level after the first NSO between low and high fuel dispensing rates during refueling operations, such as 2GPM and 12GPM. In summary, large flow windows virtually eliminate the ability to trickle fill because the vapor flow passage through the FLVV with be closed after the first NSO.
In the event of the operator needs to xe2x80x9cround upxe2x80x9d the cost of fuel to the nearest monetary unit, smaller flow windows in the housing skirt may be utilized to allow the addition of fuel during low fuel dispensing rates (commonly known as xe2x80x9ctrickle fillingxe2x80x9d); however, it is possible to overfill the tank during these multiple trickle-fill NSO""s.
Whether using large or small flow windows in the housing skirt, the ability to add fuel after a NSO is determined by whether the fuel vapor vent orifice is closed or open after a NSO. If the fuel vapor vent orifice is open after a NSO, then fuel can be added to the tank by additional NSO""s. The probability of the fuel vapor vent orifice to reopen after a NSO increases as the flow windows in the housing skirt become smaller.
It is known that the fuel level in the fuel tank, at which the fuel vapor vent orifice will close as the float rises, will decrease as the size of the flow windows in the housing skirt decreases. Theoretically, the tank fuel level at NSO will be virtually the same as the lower opening in the housing skirt when there is no flow windows at the upper end of housing skirt. This phenomena, the differences in fuel levels between that outside the housing skirt to the level inside the housing skirt, is what allows the vapor flow passage valve to cause the fuel vapor vent orifice to reopen as the flow windows in the upper portion of the housing skirt become smaller. Thus, small flow windows are required to allow the vapor flow passage valve to reopen the fuel vapor vent orifice after each NSO and to limit the addition of fuel during trickle fill operations.
However, the ability of the very small flow windows in the housing skirt to flow fuel vapor after refueling operations is limited and considered to be incapable of sufficient fuel vapor flow that is required to maintain minimal fuel tank pressure. Thus, the inventors of the present invention have discovered that there is a need to provide a means of increasing the vapor flow rate from the fuel tank to the vapor storage canister after the fuel tank has been filled to rated tank capacity as defined by multiple NSO""s during trickle fill.
An object of the present invention is to provide a feature that will vary the effective window size located in the valve assembly housing skirt above the 100% rated tank capacity fuel level in such way that the window is closed when the tank fuel level covers the bottom opening in the housing skirt(to prevent trickle-fill) and opened after multiple NSO""s to obtain minimal tank pressure after refueling operations.
In a particular illustrative embodiment of the invention, a fill limit vapor valve assembly comprises a housing including a housing skirt having first and second vent openings communicating with the interior of said fuel tank and with a fuel vapor emission device. The assembly includes a float disposed in the housing for movement in response to level of fuel. The assembly also includes a bypass valve in the housing for varying a size of the second vent opening, thereby controlling the flow rate of fuel vapor from the fuel tank to the fuel vapor emission device when the tank fuel level is above the bottom opening of the valve assembly skirt.
The bypass valve comprises a vertical passage enveloping a weighted metering rod. The weighted metering rod includes a substantially cylindrical upper portion, a substantially cylindrical bottom portion, and a seat portion that rests on a shoulder of the float. The substantially cylindrical upper portion is positioned at an elevation above the second vent opening when the float is positioned in an upward position, thereby allowing fuel vapor to pass through the second vent opening. The substantially cylindrical upper portion is positioned at approximately the same elevation as the second vent opening when the float is positioned in a downward position, thereby preventing fuel vapor to pass through the second vent opening. When the float is between the upward and downward position, the substantially cylindrical portion is portion to expose a portion of the second vent opening, thereby varying the size of the second vent opening.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.